1. Field of the invention
The present invention generally relates to a supersonic water-drop-removing mirror assembly with which water drops formed on the mirror surface are removed by vibrating the mirror and more particularly to a structure required for holding the mirror plate of such a mirror assembly.
2. Description of the related art
Hitherto, there has been provided an outside mirror assembly for use in an automobile having a function of repelling the water drops formed on and stuck to the mirror surface to lower its visibility.
With this kind of a mirror assembly, a supersonic vibrator normally attached to the backside of the mirror plate. If this vibrator is directly and fixedly attached to the mirror plate, such part of the mirror plate is not vibrated disadvantageously. Hence as seen from FIG. 7 showing the sectional structure of such a mirror assembly, the mirror plate 3 and the vibrating plate 4 behind it to which a supersonic vibrating body 6 is attached are connected in the peripheral portion by means of a connecting-member 5, thus the assembly being formed as a vibrating unit 1 of double-walled structure. In this double-walled vibrating unit 1, the mirror plate 3 and the vibrating plate 4 are made of materials equal in sound transmitting velocity so that the vibrations generated by the vibrator 6 are transmitted efficiently, the individual vibrations being of standing waves roughly equal in waveform. Specific examples of such materials may be glass for the mirror plate 3 and stainless steel or the like for the vibrating plate 4.
As to the mirror assembly for use in automobile, it has been a usual practice to hold the mirror plate 3 from behind with a mirror holder of the type extending to wrap the front periphery of the mirror plate 3 and this mirror holder is fitted in a mirror case via a universal joint. In a supersonic drop-removing mirror assembly of the aforementioned structure, however, rigidly fixing the entire periphery of the double-walled vibrating unit 1 with the mirror holder is not preferable for it means sizably dampening the vibration. With such a mirror assembly, therefore, it is necessary to take proper care to hold the periphery of the double-walled vibrating unit 1 as loose as possible by, for example, holding it at several points. In such a holding structure, however, it is possible that the mirror plate 3 is caused to move due to engine's vibration, due to bad road conditions and resultant vibration of car body running thereon or due to influence of wind the running car is subjected to or the like, this possibly resulting in accidental moving of the mirror plate 3 and lowering of mirror's visibility. Even if the double-walled vibrating unit 1 is held by point contact, it is possible that the vibration generated by the vibrator is dampened depending on the holding position, this possibly also resulting in lowering of the drop-removing performance. Meanwhile, when the vibration is of standing wave, the waveform has nodes where vibration scarcely takes place, hence it is possible that water drops cannot be removed in some parts of the mirror surface.